


Why You Shouldn't Play With Fire

by QuintessenceA



Category: Undertale (Video Game)
Genre: Aftermath of Torture, Angst, Fire Magic, Grillster, Immolation, Implied Relationships, Implied/Referenced Character Death, It could be worse but it was a bad situ to start with, Kinda bad ending?, M/M, Minor Character Death, Off-screen Relationship(s), Rape Aftermath, Rescue Missions, Sanster, Swords and Guns, Wartime
Language: English
Status: Completed
Published: 2021-02-07
Updated: 2021-02-07
Packaged: 2021-03-12 15:54:25
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,302
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29263104
Author URL: https://archiveofourown.org/users/QuintessenceA/pseuds/QuintessenceA
Summary: Intel was that Sans' platoon had been overrun. The whole team, dusted before the humans retreated. It hurt, and Grillby had seen to it that another platoon would be sent to the enemy's location in the morning to repay the favor. As much as he'd like to do it himself, he'd been given other orders and it was his responsibility to follow them.Then… word had reached Grillby- Gaster had gone AWOL.(Wartime Sanster AU)
Relationships: Implied Grillby/W. D. Gaster, Implied W. D. Gaster/Sans
Comments: 6
Kudos: 14





	Why You Shouldn't Play With Fire

**Author's Note:**

  * Inspired by [guilty or not, you pay the price](https://archiveofourown.org/works/29238123) by [hyliank8](https://archiveofourown.org/users/hyliank8/pseuds/hyliank8). 



> Full of my own headcanons for k8's Wartime Sanster AU, plus I messed with the time period, because I'm not certain When it occurs and I had ideas to make this more modern. I just wanted to imagine what would happen if Grillby came across Gaster after the events in "guilty or not, you pay the price"
> 
> I learned that there is a small, four person unit in the military called a "Fireteam". Naturally, I made Grillby lead one. Made of fire monsters- a pair of Pyropes and a blue flamed elemental.

Intel was that Sans' platoon had been overrun. The whole team, dusted before the humans retreated. It hurt, and Grillby had seen to it that another platoon would be sent to the enemy's location in the morning to repay the favor. As much as he'd like to do it himself, he'd been given other orders and it was his responsibility to follow them.

Then… word had reached Grillby- Gaster had gone Awol.

There was no doubt where he'd gone. Orders or not, Grillby had to go after him. And he was counting his lucky stars that his team had agreed to come with him. 

"Sergeant! Over here!" Davis called, waving with the tail of his rope as he ran towards the warehouse doorway. His brother, Davey, had already gone inside. 

Raine and Grillby were right behind them, and the two elementals, one blue and one orange, banked their flames as they entered the dimly lit building. The Pyrope twins, better known as the Daves, were waiting for them. Davey gestured for silence as Davis tipped his head towards the back of the building. As if on cue, the sound of raucous human laughter rang out from behind a closed door.

Grillby's Soul constricted tightly in his chest. There was no way to know what was on the other side, but something told him he was too late. _Please, lucky stars,_ he begged silently, _let me find him in one piece._

Raine crept up to the door, pressing a blue flamed hand against the flimsy barrier as she listened. She caught Grillby's eye and signaled, "three". Three humans in the room. He nodded at Davis and Davey, and they pulled their swords from their inventories. Raine's was already in her hand.

There were many theories on why monsters couldn't use guns. Everything from human intent, directly manufactured into the weapons and working against them, to the idea that human science and monster magic were just inherently incompatible. Grillby didn't know what it was, but as he pulled his own blade from his inventory he found himself remembering an old saying, "Don't bring a knife to a gun fight". Not for the first time he wished that he could wield the same weapons against their enemies that were used against them.

Until then, strike hard, and strike fast. At least the confined space should work to their advantage. Raine moved away from the door, and Grillby gave the signal, kicked the latch, and stormed into the room-

-only to be brought to a halt by what he saw.

Gaster, proud, strong Gaster, was kneeling in the center of the room, his arms bound together and strung up to the ceiling with thick, faintly luminescent rope. He was completely naked, covered only in livid, bleeding wounds. Scratches, bruises…

Human bite marks.

As Grillby struggled to understand what he was seeing, Raine burst into the room around him in a blaze of blue glory, the Daves running right behind her, flames high and swords waving. It was only when the first human screamed, Davis' sword reflecting firelight as it cut through their side, that Grillby managed to tear his eyes away.

Three humans in the room, fighting his three teammates. The Daves were currently dispatching one human, but Raine was overwhelmed, two on one. He had to move! Grillby couldn't afford the luxury of feeling horror, not while there were enemies out for their dust. With a cry, Grillby put the sight of Gaster out of his mind (Gaster was alive, that was all that mattered, he's *alive*, and everything else had to wait) and jumped into the fray.

The humans had been caught off guard, but unfortunately they weren't stupid. Their weapons were within reach, and they fought with typical human ferocity. But Grillby's team was sharp, fast, and hot. Aided by his fire magic, Grillby swung his blade at the human currently engaged with Raine. The human saw him coming, and dodged before the attack could connect.

Raine struck out at the second human as they leveled their weapon. A shot rang out, loud in the confined room, and Grillby saw Raine's form ripple as the bullet skimmed the outer layer of her flames. Her blade struck the human's hand, and he dropped the gun with a scream. It brought him close enough that Grillby could reach out, pressing a burning hand against the human's chest, sending them backwards to trip over Davey's coils. As he went down, Grillby turned his attention back to the final human.

The human's gun was pointing at his chest. The human fired.

Grillby was suddenly yanked to the side by his wrist, surprised and off balance as pain exploded through his sword arm. 

"Sergeant!" Davis yelled, loops of his rope coiled taut around Grillby's wrist. He released the tension quickly, and Grillby regained his feet.

"Thank you," Grillby said, switching his sword to his other hand. 

Another shot rang out, only this time it was followed by a cry from Gaster. 

"Hold it right there!" The human yelled, and everyone stopped. "One more move, and I'll put another hole through him, right through his head."

Slowly, Grillby turned to look at Gaster. He was sagging in his restraints, blood pouring from a fresh bullet wound in his leg. The pause gave Grillby time to better appraise the rest of Gaster's injuries. Finger print bruises from being grabbed too harshly. Bite marks from sharp human teeth. Wet trails of tears, spilling down the sides of his face. Red and purple marks, a map of torment drawn across Gaster's pale body. And something Grillby hadn't noticed before.

Globs of slimy mess, tinged with blood and leaking across the ground beneath him.

In all his hears, Grillby had never felt a fury like the one currently burning through him now. 

"Alright, monsters," the human said, sneering the word. "This is how it's gonna be. I'm gonna-"

The human cut off as Grillby roared, his flames leaping high, spilling across the room and rolling to engulf the human in the magical inferno. They screamed, ditching the gun and dropping to the ground, rolling to escape the flames.

If Grillby had the magic strength, he'd char the human to ashes. He wanted to see the human's Soul, watch it burn in his magic for what they'd done to Gaster. But even as he fed more and more magic into the blaze, he could feel it falter. War had done him no favors. There was never enough food or sleep, and no true rest to be found. The flames flickered. Grillby dropped to his knees, his sword falling from his hand as he kept pushing magic. White spots began to dance in his vision.

The flames died, and the room fell silent.

Then the human screamed out in fury. "You _FUCK!"_ They screeched, still alive. At least they sounded in horrible pain, if the labored way they breathed meant anything at all. "Just kill me!"

"Gladly," Raine called, stepping to him with her sword in the air. 

Grillby's face burned, and he thought he might be crying, but through the haze of pain and rising steam (oh, he was definitely crying) he saw the human smile. They were badly burned, skin blackened and peeling in places, but their eyes stared at Raine, bright and full of smug determination.

"Wait," Grillby shouted, and Raine stopped in mid stride. She threw him a confused look. Grillby wiped his face with his left hand (the right one wasn't working correctly, but that hardly seemed important), and the sting from his tears helped clear his head. "Don't kill them. Something… something isn't right. Something anomalous. We need to take them to Dr. Alphys."

He looked at the Daves, who stood ready, swords still out. "Can you two hold him?"

"Yessir!" "You got it, Sarge!" They yelled, dampening their flames to physically wrap themselves around the human's body.

"No! No! Fuck you!" The human spit and cursed, but he was too injured to make much resistance. His pained screeching was music to Grillby's ears. "You have to kill me! Isn't that what you damn monsters do? Show me a little goddamned mercy!"

"Be quiet," Grillby snapped, his flames surging with a pop, "before I find something to gag you with."

The human kept screaming, until Raine helped Grillby make good on his threat by picking up a discarded glove from the ground and shoving it into the human's mouth. He still howled, but it was muffled now.

The other two humans were clearly dead, and finally Grillby could move to help Gaster. He felt weak, knowing he'd pushed himself too hard with the blaze but Grillby would do it again for Gaster if he could.

"Gaster," Grillby said softly, taking off his jacket and gently, carefully laying it across Gaster's shoulders. "I've got you now, it's gonna be okay."

He had no way to know if that was true, but as he wrapped an arm around Gaster, holding him up, it felt like a lie. As soon as he was reasonably sure Gaster wouldn't tumble directly to the floor, Grillby nodded to Raine, and she cut the ropes with her sword.

Part of it fell to bounce off of Grillby's arm and he hissed in pain as the rope momentarily put out flames where it hit. Magic suppression. That was how they'd been keeping him. It was sick.

As he carefully pulled the binding from Gaster's wrists, he realized Gaster was saying something, and leaned in close.

"Sans…" Gaster said, his raspy voice barely strong enough to form the name. "Sans," he called again. Once his arm was free, he reached out past Grillby, towards the empty air, and the elemental wondered if the humans had truly broken him.

"I heard about the attack," Grillby said softly, gently pulling Gaster's arm across his shoulders. "I'm sorry."

As he and Raine carefully helped Gaster to his feet, mindful of the leg injury, Gaster looked at him, and the raw pain in his eyes was too much for Grillby to handle. He turned his head away, dropping his gaze to land on a wet mess in the center of the room. Gaster followed his eyes, and the sound he made as he stared at the gore drove through Grillby's Soul like a knife. It came with a sudden, blinding realization.

"No," he whispered, shaking his head, and Gaster made a choked, broken sound.

"What is it?" Raine asked. She looked between the two of them, the worry on her face growing.

"Hold him, please," Grillby said, slipping out from under Gaster's arm. The scientist sagged against Raine, but she kept her hold on him, even as he reached for the dust again.

It was more than enough conformation. He didn't need to look closer. He did anyway.

The wet puddle in the middle of the room… Grillby had thought it was blood. Raising his flames, his light illuminated what he should have noticed before. The mess wasn't only red.

Mixed in with the red blood were dusty streaks of fading blue.

"Sans, oh, stars Sans," Grillby stared at the remains of his friend, sickened magic twisting, churning in his body. He turned back to Gaster, searching desperately for another answer. "H-how? Sans… His platoon was defeated in the field!"

Behind him, the human began to laugh. Grillby turned to find the glove they'd gagged him with on the ground.

"The boney runt? Yeah, we kept him after we dusted his team." He shook his head in mock disappointment. "And he was a good fuck, I'm gonna mi-"

He cut off with a scream as Grillby drove a boot into his side, careful not to touch with of the Daves with his intent. Then he kicked him again. And a third time. Before he could kick him again, Grillby stepped back, watching as the man coughed up blood. He didn't think he could stop himself if he did it any more.

"Son of a _bitch_ ," the human said, quietly but vehemently. "I thought that would do it."

As Grillby stepped forward, picking up to the glove to shove it back into the human's mouth, he thought of forcing it deep enough to choke them on it.

It must have shown on his face as the human's sneer returned. "Do it," he jeered. "Kill me. You know you want to, and frankly, it'd be better for everyone."

Saying nothing, Grillby shoved the glove back into the human's mouth, and went back to help Raine with Gaster.

"Sans…" Gaster was weeping softly. "I'm sorry…"

"Come on, guys," Grillby said, getting his good arm back under Gaster. "Let's get them both out of here. There's… there's nothing else we can do here."

The Daves left first, their coiled bodies working in tandem to drag the angry, gagged and screaming human out into the warehouse, and to the outside beyond it.

Raine, Gaster and Grillby began a much slower walk out.

"Sergeant?" Raine asked after a few minutes of silence. "Are you gonna be okay?"

Grillby almost didn't hear her, his head too filled with thoughts of Sans and Gaster. They're been no mercy for Gaster, that much was clear. Sans, poor Sans. No wonder Gaster was so… broken. Stars, though Grillby had been close to both of them, he'd always known they were better together. Gaster had tried to save Sans when the army failed to protect him, only to fail himself. And now Grillby was going to fail him, because there was nothing he could possibly do to help.

He hoped Sans had died quickly. His Soul felt heavy with the obvious lie of such stupid hope.

"No," Grillby answered softly, listening to Gaster quietly cry between them. "I don't think I will be."


End file.
